Since the beginning of antiquity, both pharmacy and medicine have sought a delivery system for administering a beneficial drug. The first written reference to a delivery system is to the Eber Papyrus, written about 1552 B.C. The Eber papyrus mentions delivery systems made as dosage forms such as anal suppositories, vaginal pessaries, ointments, oral pill formulations, and other dosage preparations. About 2500 years passed without any advance in delivery system development, when the Arab physician Rhazes, 865-925 A.D., invented the coated pill. About a century later the Persian Avicenna, 980-1037 A.D., coated pills with gold or silver for increasing patient acceptability and for enhancing the effectiveness of the drug. Also around this time the first tablet was described in Arabian manuscripts written by al-Zahrawi, 936-1009 A.D. The manuscripts described a tablet formed from the follow impressions in two facing tablet molds. Pharmacy and medicine waited about 800 years for the next innovation in delivery systems, when in 1883 Mothes invented the capsule for administering drug. The next quantum leap in dosage forms came in 1972 with the invention of the osmotic delivery system by inventors Theeuwes and Higuchi as disclosed in U.S. Pat. Nos. 3,845,770 and 3,916,899. The osmotic system disclosed in those patents comprise a semipermeable wall that surrounds a compartment containing a useful agent. The wall is permeable to the passage of an external fluid, and it is substantially impermeable to the passage of useful agent. There is an osmotic passageway through the wall for delivering the useful agent from the osmotic system. These systems release a useful agent by fluid being imbibed through the semipermeable wall into the compartment at a rate determined by the permeability of the semipermeable wall and the osmotic pressure gradient across the semipermeable wall to produce an aqueous solution containing useful agent that is dispensed through the passageway from the system. These systems are extraordinarily effective for delivering a useful agent that is soluble in the fluid and exhibits an osmotic pressure gradient across the semipermeable wall against the external fluid.
A pioneer advancement in osmotic delivery systems, manufactured in the form of an osmotic device, was presented to the dispensing arts by inventor Felix Theeuwes in U.S. Pat. No. 4,111,202. In this patent, the delivery kinetics of the osmotic device are enhanced for delivering useful agents, including drugs that are insoluble to very soluble in the fluid, by manufacturing the osmotic device with a useful agent compartment and an osmagent compartment separated by an internal film. The internal film is movable from a rested to an expanded state. The osmotic device delivers agent by fluid being imbided through the semipermeable wall into the osmagent compartment producing a solution that causes the compartment to increase in volume and act as a driving force that is applied against the film. This force urges the film to expand in the device against the useful agent compartment and, correspondingly, diminish the volume of the useful agent compartment whereby useful agent is dispensed through the passageway from the osmotic device. While this device operates successfully for its intended use, and while it can deliver numerous useful agents of varying solubilities, its use can be limited because of the manufacturing steps and costs needed for fabricating and placing the movable film in the compartment of the osmotic device.
In U.S. Pat. No. 4,327,725 patentees Richard Cortese and Felix Theeuwes provided an osmotic dispensing device for delivering beneficial agents that, because of its solubilities in aqueous and biological fluids, are difficult to deliver in meaningful amounts at controlled rates over time. The osmotic devices of this patent comprise a semipermeable wall surrounding a compartment containing a beneficial agent that is insoluble to very soluble in aqueous and biological fluids and an expendable hydrogel. In operation, the hydrogel expands in the presence of external fluid that is imbided into the device and in some operations mixes with the beneficial agent, thereby forming a dispensable formulation that is dispensed through the passageway from the device. This device operates successfully for its intended use, and it delivers many difficult to deliver beneficial agents for their intended purpose. Now it has been observed, its use can be limited because the hydrogel can lack a present ability to imbide sufficient fluid for the maximum self-expansion needed for urging all beneficial agent from the device.
It will be appreciated by those versed in the dispensing art, that if an osmotic device can be provided that exhibits a high level of osmotic activity for delivering a beneficial agent by generating in situ an expanding force sufficient for delivering the maximum amount of agent at a controlled rate such as osmotic device would have a positive value and represent an advancement in the dispensing art. Likewise, it will be immediately appreciated by those versed in the dispensing art that if an osmotic device is made available possessing dual thermodynamic osmotic activity for delivering increased amounts of a beneficial agent, said osmotic device would find practical application in the fields of pharmacy and medicine.